Fig. 21. Six types of neuromuscular junction in human extraocular muscle based on electron microscopic findings. N, nucleus; A, axon; S, Schwann cell; M, mitochondrion. (Modified from Mukuno K: Fine structure of the human extraocular muscles: III. Neuromuscular junctions in the normal human extraocular muscles. Acta Soc Ophthalmol Jpn 72:104, 1968.)